Applying dense-sampling methods to reveal dynamic endocrine modulation of the nervous system.

The brain is an endocrine organ whose day-to-day function is tied to the rhythmic production of neuromodulatory hormones. Yet, traditional approaches to studying brain-hormone relationships in humans are often coarse in scope. By contrast, dense-sampling neuroimaging offers the unique ability to probe dynamic interactions between the nervous and endocrine systems. This review summarizes recent evidence of sex hormones' influence on structural and functional properties of the human brain. In particular, findings from the '28andMe' project suggest that estradiol modulates the topology of large-scale functional brain networks and progesterone rapidly shapes medial temporal lobe morphology across the menstrual cycle. This nascent body of work sets the stage for additional studies in larger cohorts. We end by discussing the potential of dense-sampling designs to further elucidate endocrine modulation of the brain, with implications for personalized medicine.